Patent Grant
11105508
The disclosure relates generally to a flare burner for the burning and disposal of combustible waste gases and more particularly, to a flare burner having a tip which reduces the exposure of ancillary equipment to thermal radiation.
Gas flares are commonly located at production facilities, refineries, processing plants, and the like for disposing of combustible waste gases and other combustible gas streams that are diverted due to venting requirements, shut-downs, upsets, and/or emergencies. Such flares are often operated in a smokeless or near smokeless manner, which can be largely achieved by making sure that the flammable gas to be discharged and burned (“flare gas”) is admixed with enough air to sufficiently oxidize the gas. Pressure assisted multipoint ground flares (MPGF) have long been used in the petrochemical industry, as well as gas plants and refineries for the safe disposal of vent gases during upset conditions. A properly designed MPGF can achieve 100% smokeless operation under all flow conditions for which it has been designed. This type of flare has low public profile compared to a typical elevated flare because these systems may have no visible flame outside the plant. Additionally, the higher destruction efficiency of an MPGF can significantly reduce continuous plant emissions. These flare systems are comprised of a radiation fence—also known as a wind fence—a distribution manifold with fail-open valves, multiple smaller manifolds (or runners), which terminate in flare burners, and a control system that operates the staging valves based on the supply pressure. Surrounding the field is the radiation fence. In the foreground, the elevated and shielded horizontal pipes Gust above grade) are the runners and the burners are mounted on the smaller vertical pipes.
A typical flare apparatus includes one or more flare burners and a pilot. As gases exit the flare burners, the gases mix with the oxygen and combust (via the flame from the pilot). Some flare burners use various methods in an attempt to provide sufficient oxygen in a combustion zone of a flare burner to help minimize the formation of smoke.
For example, in some flare burners, the size of the flare burner is larger. However, as a result of the large size of the flare burner, a significant amount of ground space is often required for the flare burner. This problem is increased when multiple flare burners are used, with the burner array requiring a large area of ground space.
In some flare burners, the flame that is produced is very high. Not only is the high flame height undesirable, but the high flame height requires a higher fence around the flare burner area. The higher fence is more expensive. The higher flow of waste gas in the center of the flare tip can also increase the oxygen requirements at the center of the flare tip. This can increase the propensity of the flare to smoke.
Furthermore, many large flare burner areas require a large amount of piping and multiple valves. The required piping and valves increase the capital cost associated with the flare burner. Additionally, these types of flare burners also may require welded joints and attachment points. This results in a flare burner that is complex to assemble and costs more.
In addition, many flare burners are noisy mainly due to both jet noise and combustion noise. While the jet noise (the noise associated with the speed of the gases exiting the burner) may not be able to be lowered, it is believed that the combustion noise (associated with the mixing of the air and fuel gases) can be lowered and still provide an acceptable flame.
In addition, it has been found that flares that are located in close proximity to ancillary equipment may cast substantial amounts of thermal radiation on the equipment during normal operation. If a flame center of radiation is moved closer to such equipment as fences, the radiation will increase and equipment may be damaged. This invention solves the problem by utilizing an asymmetrical disposition of fuel gas combined with an offset riser such that a substantial portion of the radiation is cast away from the ancillary equipment to grade.
Some fuel gas is still in vertical alignment with the distribution manifold in order to facilitate cross-lighting of individual flare burners.
An additional issue is that frequently multiple burners are used. When multiple burners are used in conjunction the momentum of the flames flowing in unison tends to merge them together and increase their length due to a lack of access to air. In the case of a multi-point flare this can mean that burner flames that are in isolation would have a length less than that of the surrounding radiation fence can merge and have a resultant length that is taller than that of the radiation fence.
Pressure-assisted flare burners rely on high velocity vent gas jets for the entrainment of combustion air to provide smokeless operation. The minimum pressure, and therefore minimum port exit velocity, at which the burner can operate without producing smoke from the flame is a critical design feature.
A lower smokeless operating pressure for a flare burner results in a wider operating range for a given stage, so, therefore, can reduce the number of stages required for a properly functioning smokeless flare field. There is an additional benefit of reduced heat load on the flare components due to adequate vent gas and air mixing even at low flows. The de-staging pressure is the minimum operating pressure of the flare system for which smokeless performance should be expected. The maximum operating pressure that produced smoke for any vent gas tested was 42% of this de-staging pressure. Accounting for the variability among the tested vent gases, there is a 0.01% (122.87 ppm) chance of visible smoke across vent gas types during a de-staging event. The probability of visible smoke from the flare burner is less than the statistical analysis suggests, given that the most common type of vent gas that produces the most smoke is contained within the data set at 42% of the de-stage pressure. Although visible smoke could occur near the burner, it still may not rise above the flare fence before dissipating. The Galaxy burner produces essentially no visible smoke for any of the vent gas compositions tested.
Therefore, it would be desirable to have a flare burner for combustible gas that addresses each of these issues.
Various designs for flare burners for combustible gases have been invented to provide an effective flare burner that can provide increased mixing between the surrounding air and the combustible gas, without some of the drawbacks discussed above.
In one aspect of the present invention, the invention may be characterized as a flare burner for burning combustible waste gases. The burner comprises a manifold comprising an inlet, a plurality of arms, and a plurality of outlets. The inlet is configured to be secured to a conduit for combustible waste gases. The plurality of outlets is disposed on a plurality of arms such that oxygen may mix with combustible waste gases exiting the outlets. The flare tips are oriented so that about ⅓ of the fuel gas is disposed over the manifold and about ⅔ of the fuel gas is oriented over grade and away from the equipment.
In at least one embodiments of the present invention, the manifold of the flare burner comprises a body extending in a first direction having a longitudinal axis parallel thereto. The arms from the plurality of arms each have a longitudinal axis extending along a length of a body, and the longitudinal axes of the body are relatively perpendicular to the longitudinal axis of the body of the manifold.
In another embodiment, the manifold of the flare burner comprises a body and a curved dispersing surface disposed in a middle of the body of the manifold. The arms from the plurality of arms extend radially outward from the body.
In one or more embodiments of the present invention, the manifold of the flare burner comprises a body. A first annulus surrounds the body and a second annulus surrounds the body. The arms from the plurality of arms extend radially outward from the body into the first annulus and the second annulus. It is contemplated that the burner further includes at least one baffle in the first annulus configured to impart a direction of rotation to air within the first annulus and at least one baffle in the second annulus configured to impart a direction of rotation to air within the second annulus. The direction of rotation of gas exiting the first annulus is opposite the direction of rotation of gas exiting the second annulus.
In at least one embodiment of the present invention, the manifold of the flare burner comprises a body. The arms from the plurality of arms extend radially outward from the body. A first end of each arm is disposed adjacent the body of the manifold and a second end of each arm is split into two branched portions. It is contemplated that each branched portion is split into two more branched portions. It is even further contemplated that an outlet is disposed at each end of each branched portion. It is even further contemplated that a collar is surrounding each outlet to provide a swirl to combustion gases exiting therefrom.
In some of the embodiments of the present invention, the manifold comprises a body. The arms from the plurality of arms extend radially outward from the body and each arm includes a first portion without any apertures and a second portion with one or more apertures. It is contemplated that at least the second portion has a curvilinear shape and the first portion and the second portion have approximately the same length. It is contemplated that the arms extend upwardly away from the body of the manifold. It is also contemplated that the arms extend downwardly away from the body of the manifold. It is still further contemplated that each arm has a cross-sectional shape comprising a top rounded portion and a tail portion comprising two intersecting linear edges.
In one or more embodiments of the present invention, each arm includes a plurality of outlets and the outlets on each arm are disposed such that a distance between the manifold and an outlet closest to the manifold on that arm is greater than a distance between any two outlets on that arm.
In some embodiments of the present invention, each arm includes a plurality of outlets and the outlets on each arm are disposed about a circumference of a circle. A distance between the manifold and an outlet closest to the manifold on that arm is greater than a radius of the circle. It is contemplated that the outlets on each arm are spaced at least 11° from adjacent outlets.
In various embodiments of the present invention, each arm includes a plurality of outlets with a width being the distance between two furthest apart outlets on that arm and the width is smaller than a distance between the outlets on that arm and outlets on adjacent arm.
In at least one embodiment of the present invention, each arm includes a plurality of outlets, and the outlets on each arm are separated from adjacent outlets by a wall having a height between one to five times a diameter of the outlets. It is contemplated that the outlets of each arm are disposed on a portion of an arm that has a cross-sectional shape comprising a top rounded portion and a tail portion comprising two intersecting linear edges.
In some embodiments of the present invention, each arm includes an inlet and the inlets are disposed within the manifold and the inlets of the arms intersect.
Additional objects, embodiments, and details of the invention are set forth in the following detailed description of the invention.
The attached figures will make it possible to understand the various embodiments of the present invention can be produced. In these figures, identical reference numbers denote similar elements.
Various new flare burners have been invented which provide for improved gas flow. The new flare burners distribute the flame on a larger surface and more evenly provide the required combustion air. When the flame receives air more evenly, there is better mixing of the fuel and the air and a minimization of fuel rich zones which can generate smoke. Additionally, when the flame is distributed on a larger surface the flame is shorter compared to a traditional system with the same output. Consequently, the output will be greater compared to a system with the same maximum flame length. Furthermore, the footprint area of the whole flare array is smaller compared to a system with the same output and same max flame length. These and other benefits will be appreciated based upon the following detailed description.
A typical multipoint flare stage may have between five and 50 burners attached to a single pipe manifold. When a stage is placed in service, a continuously burning pilot ignites a flare burner. The flame then propagates—or cross-lights—the row of burners comprising a stage. If there is a delay in the lighting of the burners, a higher volume of combustible vent gas will accumulate near the burner heads before ignition occurs, potentially resulting in an audible pressure wave during the ignition event. To reduce the ignition delay between flare burner heads, cross-lighting ports can be used to direct ignited vent gas to the adjacent flare burner head. For vent gas with a large inert mixture component or low flame speed, the size of the ports required for cross-lighting may disturb the air ingress and mixing between the flare burner heads under full load, which could cause flames to rise above the radiation fence.
Additionally, a large portion of the heat may be released directly adjacent to the burner heads, reducing their life either through direct heating or coke production from the heated vent gas inside the burner heads. Another common solution to decrease the time delay in cross-lighting is to move the flare burner heads closer together along the length of the vent gas distribution manifold. For older burner designs, the combined flame of multiple burners operating at high capacity would often be visible above the flare fence. However, the multipoint flare burner was designed from inception to operate as part of a large flare system while maintaining short flame lengths.
Multipoint flares use a radiation barrier, or ‘wind fence’, to achieve safe near-field thermal radiation levels. Direct exposure to radiation from the flames, at full vent gas flow rates, would ignite most flammable objects in the immediate vicinity. In most applications, there should be no visible flame over the top of the radiation fence under any circumstances in order to minimize flare visibility, radiation and community impact. The burners of the present invention provide about a 20% shorter flame as compared to the previous generation burner, while flowing about 1.5 times as much vent gas. The flame height may be reduced as required on a per application basis, depending upon the vent gas composition. Flare systems that use this type of flare burner can use shorter radiation fences and fewer burners. The height of the flame for an equivalent flow rate has been significantly reduced compared to previous generations of burners.
One of the basic design tenets of a multipoint flare field is a reduction in the flame length from the entire vent gas flow. This produces a more manageable flame size by exhausting the vent flow through many smaller flames, as opposed to one large flame. Breaking a single jet into multiple jets increases the mixing rate of the vent gas with the surrounding air, resulting in smaller jet dissipation length. In the case of injection of multiple jets, it has been established that the flow from the jets will merge. If the flows from each individual burner merge before combustion is complete, the zone where the flows touch becomes starved for air and the flames become longer. For this reason, the flames from multiple burners will be longer than the flame from a single burner. The flare burner of the present invention has a unique feature that alleviates elongated flames in multiple burner installations. An asymmetrical gas injection pattern ensures that, where the flames must touch for smooth and efficiency cross-lighting, ultimate flame length does not become longer than that of a single burner flame. This feature has been tested in multiple burner physical testing, and then extensively evaluated using computational fluid dynamics (CFD). The burner may be made from cast high alloy steel and preferably is a single-piece design with no welds in the heat affected zone. This design modification has been made based on industry experience after the failure point of many types of multipoint flare burners occurred where welds had been made to either attach arms to a spider burner, or to affix a top-plate to an open casting. Tests were performed to confirm the burner's robust design. The maximum thermal stress induced falls well below the failure point of the material, even under the continuous steady-state operation of a single burner at maximum flow rate. An increased smokeless turndown capability, improved burner cross-lighting, reduced specific flame length per unit of vent gas flow, and high vent gas destruction efficiency afford many system-wide design improvements. The burner count for the flare system can be reduced due to the increased smokeless turndown capability, improved cross-lighting and shorter flame length. A lower burner count results in a reduced spare parts requirement, decreasing the initial capital expenditure and the operating cost of the flare system. A shorter specific flame length per unit of vent gas flow can also use a shorter radiation fence. The burner flame length does not increase in multi-burner installations to the same degree as previous generation burners, allowing for a more reliable flame tip location relative to the top of the flare fence. In addition to the reduced material cost of a shorter fence, the reduced weight results in reduced foundation requirements.
With reference to the attached drawings, one or more embodiments of the present invention will now be described with the understanding that the described embodiments are merely preferred and are not intended to be limiting. It is contemplated that the flare burners of the present invention can be used in other flame burning applications beyond a flare array and may simply be used as a single flare burner for simply disposing or combusting unwanted gas.
As shown in
As shown in
The outlets 18 are preferably disposed on the upper surface 24 of the arm 16 and can be drilled or cast. The size of the outlets 18 (preferably between 1/16 inch and ¼ inch) as well as the location of the outlets 18, can be optimized according to the application. The length of the arms 16 should be so that most of the area of the flare burner 10 is evenly spaced enough between the outlets 18 to allow sufficient entrainment of the surrounding air with combustible gas exiting via the outlets 18. It is believed that an appropriate spacing between adjacent outlets 18 is approximately three times the size (or area) of the outlet 18.
Turing to
As shown in
The first plurality of outlets 118a (closest to the body 120 of the manifold 112) is used to establish flow along a surface 132 of the curved dispersing surface 128. This will aerodynamically spread the flow of combustible gas and entrain more of the surrounding air therewith. The second plurality of outlets 118b (further from the body 120 of the manifold 112) are disposed to allow the combustible gas to impinge the surface 132 of the curved dispersing surface 128 in a delayed manner. This will allow the combustible gas from the second plurality of outlets 118b to entrain more of the surrounding air before impinging on the surface 132 of the curved dispersing surface 128. This partially-premixed gas mixture then flows along the surface 132 of the curved dispersing surface 128. Due to the jet expansion that occurs in a direction away from the curvature of the surface 132, a higher velocity of the mixture is maintained delaying the onset of combustion while a greater portion of air is entrained into the gas flow.
With reference to
Each arm 216 includes at least one outlet 218 disposed in the first annulus 234 or disposed in the second annulus 236. Alternatively, each arm 216 may include at least one outlet 218 in each of the first annulus 234 and the second annulus 236. The outlets 218 may be angled upwards to direct the flow of combustion gases exiting therefrom.
As the combustion gases exit the outlets 218, the combustion gases will flow around through either the first annulus 234 or the second annulus 236. A rotational direction of combustion gas exiting the first annulus 234 is preferably opposite a rotational direction of combustion gas exiting the second annulus 236. For example, in
It is preferred that each annulus 234, 236 includes one or more baffles 238 to further impart a rotational direction to the gas exiting the outlets 218 and ultimately exiting out of the tops of each annulus 234, 236. The baffles 238 also increase the speed of the surrounding air flowing up through each annulus 234, 236 and mixing with the combustion gas therein. The high-pressure gas is used to entrain and partially premix a portion of the surrounding air with the combustible gases exiting the outlets 218. This entrainment is done inside of the first annulus 234 and second annulus 236 in association with the baffles 238.
In current designs, fuel mixing with the air stream is produced by shear mixing with the quiescent air. However, using the fuel to produce a forced-shear zone between the first annulus 234 and second annulus 236 is believed to enhance mixing between the fuel and the air. It is preferred that the opposite-direction momentum is destroyed, for example, with turbulence. A proper balance between the first annulus 234 and second annulus 236 should produce a net-zero spin. After the rotational component of the mixture is reduced, the upward component of the gas flow momentum should be maintained after mixing. Slight premixing may be by placing the outlets just below the tops of the first annulus 234 and second annulus 236.
In
The outlets 318 are disposed on the branched portions 344 of the arms 316. See,
It is preferred that the outlets 318 are configured to provide a swirl to combustible gases exiting therefrom. Therefore, as shown in
Turning to
As can be seen, the arms 416 are angled upwards as the arm 416 extends further away from the body 420 of the manifold 412. It is also preferred that the vertical size of the arms 416 is reduced as the arm 416 extends further away from the body 420 of the manifold 412. This flare burner 410 is made from a single piece, and preferably does not include welds.
With reference to
A top surface 522 of each arm 516 includes a plurality of outlets 518. Preferably, the outlets 518 are drilled into the arms 516 of the flare burner 510. Additionally, the outlets 518 can be configured to expel combustible gas generally perpendicular to the ground or at a different angle (acute or obtuse) to the ground.
It is preferred that the top surface 522 of each arm 516 includes a first portion 556 without any outlets 518 and a second portion 558 with one or more outlets 518. The first portion 556 of the top surface 522 and the second portion 558 of the top surface 522 may have approximately the same length. It is contemplated that the first portion 556 without any outlets 518 or the second portion 558 with the outlets 518 are linear.
As shown in
As shown in
Turning to
As can be seen in
Turning to
Turning to
The outlets 718 on the arms 716 may be drilled prior to assembling the flare burner 710. Preferably, the outlets 718 are disposed on the upper surface 722 of the arm 716 approximately about a circumference of a circle.
Additionally, as can be seen in
With reference to the flare burner 610 shown in
For example, if the outlets 618, 718 are disposed about a circumference of a circle, the outlets 618, 718 on each arm 616, 716 are preferably spaced at least 11 degrees from adjacent outlets 618, 718. See,
Additionally, a distance D2 between the manifold 612, 712 and an outlet 618, 718 closest to the manifold 612, 712 on an arm 616, 716 is preferably greater than a distance D3 between any two outlets 618, 718 on that arm 616, 716. See,
It is also contemplated that, a plurality of outlets 618, 718 on an arm 616, 716 have a width W2 defined as the distance between two furthest apart outlets 618, 718 on that arm 616. See,
Walls 664 from
Some of the advantages of one or more flare burners shown herein is that it is cost effective, easy to build, modular, it is has small volume for shipping and storing by stacking. Additionally, the outlet configuration is customizable allowing for specific configurations which can be more efficient.
Any one of these flare burners according to the present invention is believed to provide for better gas flow to the flare burner so that sufficient oxygen in the surrounding atmosphere can mix with the gases exiting the flare burner. This improved mixing has significant direct and indirect benefits that address the problems associated with current designs.
For example, by providing sufficient air and sufficient mixing in the lower portion of the flame close to the burner, the flame may be shorter, and the combustion optimized.
A shorter flame will allow considerable cost savings, because the burner duty can be increased without increasing the height of the fence surrounding the flare system, as well as requiring less flare burners and, accordingly, less space for a flare system.
In sum, the various designs of the present invention provide for flare burners that address various shortcomings of the current designs. Any single design may alleviate one or more problem, and the various aspects and features of the designs may be combined to alleviate other problems.
It should be appreciated and understood by those of ordinary skill in the art that various other components were not shown in the drawings as it is believed that the specifics of same are well within the knowledge of those of ordinary skill in the art and a description of same is not necessary for practicing or understating the embodiments of the present invention.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.
This application is a Continuation of U.S. patent Ser. No. 15/798,301, filed on Oct. 30, 2017, which claims priority from Provisional Application No. 62/415,980 filed Nov. 1, 2016, the contents of both of which are hereby incorporated by reference in their entirety.
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| Number | Date | Country | |
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| Parent | 15798301 | Oct 2017 | US |
| Child | 16781392 | US |
